1. Field
The present invention relates in general to seals for multistage turbomachines. In particular, embodiments of the present invention relate to an anti-rotation structure for a belly band seal provided between adjoining disks in a multistage turbomachine, and to a method for assembling such a bellyband seal.
2. Description of the Related Art
In various multistage turbomachines used for energy conversion, such as turbines, a fluid is used to produce rotational motion. In a gas turbine, for example, a gas is compressed through successive stages in a compressor and mixed with fuel in a combustor. The combination of gas and fuel is then ignited for generating combustion gases that are directed to turbine stages to produce the rotational motion. The turbine stages and compressor stages typically have stationary or non-rotary components, e.g., vane structures, that cooperate with rotatable components, e.g., rotor blades, for compressing and expanding the operational gases.
The rotor blades are typically mounted to disks that are supported for rotation on a rotor shaft. Annular arms extend from opposed portions of adjoining disks to define paired annular arms. A cooling air cavity is formed on an inner side of the paired annular arms between the disks of mutually adjacent stages, and a labyrinth seal may be provided on the inner circumferential surface of the stationary vane structures for cooperating with the annular arms to effect a gas seal between a path for the hot combustion gases and the cooling air cavity. The paired annular arms extending from opposed portions of adjoining disks define opposing end faces located in spaced relation to each other. This space between the opposing end faces of the adjacent rotor disks is sealed by a seal structure commonly referred to as a “belly band seal”. The belly band seal includes a seal strip which bridges the gap between the opposing end faces of the adjoining rotor disks to prevent cooling air flowing through the cooling air cavity from leaking into the path for the hot combustion gases. The seal strip may be formed of multiple segments, in the circumferential direction, that are interconnected at lapped or stepped ends.
When the seal strip comprises plural segments positioned adjacent to each other, in the circumferential direction, under thermal load the seal strip may shift tangentially (i.e., along a circumferential direction) relative to each other. Shifting may cause one end of a seal strip segment to increase the overlap with an adjacent segment, while the opposite end of the seal strip segment will move out of engagement with an adjacent segment, opening a gap for passage of gases through the seal strip. In order to prevent rotation of the seal strip segments, the segments may be provided with anti-rotation structures to cooperate with an adjacent disk surface for holding the segments stationary relative to the disk.
Anti-rotation structures typically constrain the seal strip at the center of the seal strip segment. Known configurations for an anti-rotation structure includes a pin configuration, bend tab configuration, lock-block configuration, u-clip configuration and T-block configuration, among others. Among all of the above configurations, the pin configuration provides relatively high design life, typically about 18,000-50,000 hours. However, a belly band seal having an anti-rotation structure with a pin design can only be installed when the rotor is de-stacked.